Girls: what if he was older than he looked?

I've been told numerous times that I look young for my age which is fucking great, it's flattering. I just want to make it clear I'm not necessarily looking for the younger crowd either; if she can hang with me in conversations, she's in.

A new guy at work whom was 19 years old asked me how old I was. I gave him my age and he replied with mockery, "Yeah, and I have six kids." (again, he's 19) as if to say he didn't believe me.

Another guy, just the other day, got to asking my age because I called him a youngyun, he's 23 years old. He was convinced I was younger than him and proceeded to ask for my ID which I didn't provide.

So yeah, going back to my question: how would girls react to dating a guy whom you thought was in his early 20's when in fact he's daddy material, haha?